I bought a Trek 7500 this spring. I don't like it. It feels sluggish compared to my friend's mountain bike (a $350ish Trek), which I don't understand at all. Also, I don't think it fits me, despite what the salesperson at the LBS says. I'm a total cycling novice, so I don't know what the the root problem is.
I would recommend buying something used from
www.craigslist.com. If you love it, great; if you hate it, at least you didn't pay retail.